${4 \div 0.4 = {?}}$
Solution: $ {4 \div 0.4 = 4 \div \dfrac{4}{10}} $ $ {\phantom{4 \div 0.4} = 4 \div \dfrac{2}{5}} $ Dividing by a fraction is the same as multiplying by the reciprocal of the fraction. $ {4 \div \dfrac{2}{5} = 4 \times \dfrac{5}{2}} $ $ {\phantom{4 \div \dfrac{2}{5}} = \dfrac{4 \times 5}{2}} $ $ {\phantom{4 \div \dfrac{2}{5}} = \dfrac{20}{2}} $ $ {\phantom{4 \div \dfrac{2}{5}} = 10} $